In recent years, hybrid motor vehicles configured to travel by using a driving force generated by an electric motor in addition to an engine power have been developed (see Japanese Laid-Open Patent Application Publication No. 6-64451). Such hybrid vehicles have been commonly applied to four-wheeled motor vehicles and are now expected to be applied to two-wheeled motor vehicles.
When an electric motor is incorporated into a motorcycle, it is desirable to dispose the electric motor in a location where the electric motor is less susceptible to disturbances in the environment for the purpose of stable operation, because the electric motor operates on electric power. Furthermore, it is necessary to mount the electric motor efficiently in a limited space of the motorcycle so as not to increase the size of a vehicle body of the motorcycle.